Diaphragm-type seals have been employed in the past in rotary seal applications, such as, between a rotating axle and a spindle housing in a motor vehicle. For example, U.S. Pat. No. 4,502,698 to M. T. Collins, entitled "ROTARY FACE SEAL WITH FLEXIBLE ANNULAR BOOT" and assigned to the assignee of this application, discloses a boot mounted in surrounding relation to a shaft or axle and terminating in an outer peripheral seal ring which has a tapered face engaging the radial wall of the outer stationary spindle housing; and a spring member urges the seal ring into firm engagement with the radial wall, the boot being free to be radially displaced in response to axial and radial movement of the axle with respect to the housing so that the seal ring will remain seated notwithstanding any pulsating or translational movement of the axle while maintaining a constant pressure over its entire circumference. In the said U.S. Pat. No. 4,502,698, the boot is of a generally S-shaped construction, and the entire seal assembly as described is effective to prevent contaminants from advancing past the radial wall of the spindle housing and into contact with the axle and other components; and, further, the boot prevents the flow of lubricating grease out of the inboard side of the spindle thereby aiding in long term protection of components both inboard and outboard of the spindle.
Generally, for most effective sealing, constant pressure should be maintained over the entire circumference of the face portion of the seal ring notwithstanding axial misalignment or eccentric orbiting which may occur as the shaft spins. Thus, it is desirable that the seal ring be so constructed and arranged as to establish a thin annular band of contact at its sealing surface with a surface to be sealed. This thin band of contact results in optimum sealing conditions and prevents contamination as well as excessive wear of the seal face otherwise occasioned when the axially directed force is spread over a more limited surface area on the seal face. The thin band of contact also has been found to establish improved sealing notwithstanding imperfections in the surface to be sealed and high rates of shaft rotation resulting in application of centrifugal forces which are exerted outwardly upon the seal ring and face. Further, it is important that the seal face be axially loaded or biased in such a way as to remain in contact with the surface to be sealed irrespective of forces exerted upon the seal face and changes in atmospheric pressure or other pressure changes which may occur as a result of translational shaft movement or sudden changes in temperature.